President Nayib Bukele imposed a state of emergency in March 2022 that has seen tens of thousands of alleged gang members rounded up -- a move popular among residents, but which has alarmed rights groups.

Security forces have on several occasions besieged key cities to carry out house-to-house searches for gang members, but it is the first time an entire department is being cordoned off.

"Since this morning, 7,000 soldiers and 1,000 police officers have established a security fence around the entire department of Cabanas," Bukele wrote on Twitter, now called X.

"Their job will be to prevent gang members from leaving the area and cut off all supply lines belonging to terrorist groups."

Bukele said that Cabanas had in recent weeks become a refuge for gang cells fleeing his crackdown.

He said the blockade would last until "the operatives can extract all gang members."

Cabanas is a small, agricultural region that is home to some 150,000 people.

Trucks loaded with soldiers were seen in the streets of the towns of Tejutepeque and Ilobaso.

"Since this morning we have noticed the presence of soldiers," radio host Reina Navarrete told AFP from another town, Victoria.

Bukele imposed the state of emergency, which allows arrests without a warrant, after a particularly bloody weekend in March 2022 left 87 civilians dead at the hands of gang members.

Since then, some 72,000 alleged gang members have been arrested.

Last week, lawmakers passed a temporary measure allowing for up to 900 people to be tried at once.

Collective trials will further violate "the rights to an adequate defense, to a fair trial and the presumption of innocence," Amnesty International Americas director Erika Guevara Rosas told AFP.